The invention relates generally to the field of power control systems. More specifically, the invention relates to an insulating support flange for eliminating partial discharge in a current loop system.
Motor controllers, and more generally, electrical controllers operate by limiting the power from a power supply that reaches a motor or other load. For example, some motor controllers limit the power delivered to a motor by intermittently conducting current between the power supply and the motor. These motor controllers typically couple to a sinusoidal alternating current (AC) power supply and conduct current during a portion of each cycle of the sinusoid. Correspondingly, to limit the power delivered to the motor, the motor controller may not conduct current during a portion of each cycle. Typically, the duration of the period during which the motor controller does not conduct current is adjustable. Consequently, by adjusting the duration of this non-conductive period, the operation of the motor may be controlled.
Some motor controllers selectively transmit power by conducting current through a pair of silicon controlled rectifiers (SCRs). An SCR is a type of solid state switch that includes a rectifier controlled by a gate signal. Thus, when turned on by the gate signal, the SCR permits current to flow from its anode to its cathode but not in the reverse direction. Once turned on, the SCR typically remains on until the gate signal is removed and the current decreases to near zero. In the off state, the SCR usually does not conduct current in either direction. By applying a gate signal at the appropriate times, a motor controller may regulate the power delivered to a load.
Typically, a motor controller includes circuitry for turning on the SCRs. A motor controller may include a driver that delivers a small current to the gate electrode of an SCR. The driver may time the pulse of current to the gate electrode to regulate the power delivered to the motor. To deliver more power, the driver will delay for less time after an SCR becomes forward biased before turning on the SCR. Similarly, to reduce the power delivered to the motor, the driver will delay a longer period after an SCR becomes forward biased before turning on the SCR and permitting current to pass. Each driver includes circuitry for determining when to turn on the SCR. Typically, motor controllers employ one driver for each SCR. Thus, a motor controller regulating a single phase of AC power typically employs two drivers, whereas a three phase controller includes six.
Powering the operation of the drivers presents challenges. Often, the drivers connect to an SCR that is exposed to high voltages. For example, SCRs often connect to power supplies that operate at 2300 volts or higher. Thus, it may be important to keep the driver electrically isolated from other parts of the system. Some systems employ a single power supply for each driver. However, dedicated power supplies for each driver may add to system costs, the size of the system, and the number of components that may fail. Moreover, motor controllers often employ a large number of drivers. For example, as noted above, a motor controller that regulates power from a three phase AC power supply may employ six drivers, one for each of the two SCRs for each phase. Similarly, to regulate the power from higher voltage power supplies, a motor controller may employ two or more pairs of SCRs for each phase. Thus, a three phase system with three SCR pairs for each phase may employ 18 SCRs and 18 drivers. Consequently, powering each driver with a dedicated power supply becomes less desirable as the number of switches and drivers increases.
With some success, designers turned to self-powered gate driver systems (SPGDSs) to avoid these issues. Typically, SPGDSs capture energy from the power supply driving the load (i.e., line power). Often, within an SPGDS, a series of capacitors connect to self-powered circuitry that charges the capacitors. The SPGDS may exploit voltage differentials across the SCRs to draw current and store a charge. The charge on the capacitors can then be used to power the drivers. The voltage differentials exploited to charge the capacitors typically occur during the operation of the SCRs. As the SCRs intermittently conduct current between the power source and load, a voltage differential may form across the SCRs. A self-powered system may avoid the isolation issues associated with dedicated power supplies for each driver. Also, the cost of the components directed toward powering the drivers may be lower in a self-powered system than in a system employing dedicated power supplies for each driver. However, SPGDSs are in need of improvement because it is now recognized that SPGDSs are associated with delays in operation and response time.